Vehicle bumper beam comprising a crosspiece and two shock absorbers

ABSTRACT

The invention concerns a vehicle bumper beam comprising a crosspiece ( 6 ) and two shock absorbers ( 8 ) fixed at two respective portions of the crosspiece and made with a material different from the material of the crosspiece. The shock absorbers are made of synthetic material.

The invention relates to bumper beams for motor vehicles, in respect ofboth front bumpers and rear bumpers.

It is known that the behavior of vehicle bumpers in the event of impactcan be studied by means of various tests that are more or lessstandardized as a function in particular of the regulations in force inEurope and the United States of America. There are essentially four ofthese tests.

Firstly, there is the test known as the “parking impact” test. It iscarried out at four kilometers/hour in Europe and at eightkilometers/hour in the United States of America. During this test, onlythe bumper absorber should deform without damaging the bumper beamitself.

Another of these tests is that known as the “pedestrian impact” test. Itaims to as far as possible reduce the injuries caused to a pedestrianwhen struck by a vehicle at low speed.

Another of these tests is that known as the “urban impact” test. InEurope this is also referred to the as “DANNER” impact or “reparabilityimpact” test. During this test, the vehicle strikes a solid wall at aspeed of sixteen kilometers/hour, the wall extending over 40% of thewidth of the vehicle. During this impact, the bumper must be primarilydamaged so as to preserve the chassis of the vehicle, in particular theside rails.

Finally, the fourth test is that known as the “high speed impactcompatibility” test. During this test, the vehicle strikes a barrierthat covers 40% of the width of the vehicle, at a speed of sixtykilometers/hour. This standardized barrier comprises a deformable bufferstop made of aluminum with a honeycomb structure of 50 psi (compressionpressure), this buffer stop being followed by a wall having a honeycombstructure also of 50 psi. During this impact, the bumper beam mounted onthe side rails of the vehicle must be capable of deforming the barrieruniformly without breaking the latter. It is particularly important thatthe side rail of the vehicle does not break the barrier. The beam mustnot break and must deform the barrier so that it does not bear againstthe engine. It is therefore necessary that the beam deforms the bufferstop, starts to deform the barrier and, without breaking the beam andduring crushing of the barrier, the side rail itself begins to becrushed. Once the beam is bearing against the engine, it is consideredthat it has performed its function. In order not to perforate thebarrier with the side rail, the force has to be distributed over theentire bearing surface of the beam. It is also necessary to prevent thebeam from wrapping itself around the barrier. In order to successfullypass this test, the beam must be rigid so as to distribute the forcesover the barrier.

In this context, bumper beams made of steel or aluminum have beenproposed. However, steel beams prove to be very heavy whereas aluminumbeams are relatively expensive.

Beams made of composite material based on a plastic possibly reinforcedwith glass fibers have also been proposed. However, these beamsgenerally are not sufficiently resistant to impact. They break into anumber of pieces or else are not sufficiently rigid to deform thebarrier in the event of a high-speed impact.

There has also been proposed a beam formed of an aluminum profiled partand two steel absorbers which are designed to be fixed to the side railsof the vehicle and to be compressed in the event of an impact of the“reparability impact” type. The use of aluminum in such a beam makes itpossible to reduce its weight. Moreover, steel absorbers are inexpensiveto mould and have a compression ratio that is greater than they wouldhave if they were to be made of aluminum. However, this beam is stillrelatively heavy and the absorbers are still relatively voluminous.

One object of the invention is to provide a bumper beam which respondswell during the various impacts mentioned above and does so withouthaving either a prohibitive weight or a prohibitive volume or aprohibitive cost.

For this purpose, there is provided according to the invention a bumperbeam for a vehicle, comprising one crossbar and two shock absorbers thatare attached to two respective portions of the crossbar and are formedin a material that is different from a material of the crossbar, theabsorbers being made of synthetic material.

Thus, absorbers made of synthetic material make it possible to reducethe weight of the beam in comparison with absorbers made of steel. Thisgain may be up to 50% if the absorbers are made of composite material.Moreover, the absorbers of the beam according to the invention have acompression ratio greater than that of steel, which makes it possible toreduce their volume at rest while absorbing the same amount of energy inthe event of an impact. It is therefore possible to give cars a morecompact style. The absorber made of synthetic material is particularlyuseful in the case of the “reparability impact”.

More specifically, the compression ratio corresponds to the ratiobetween the crushing travel of the absorber (without an increase inforce greater than the resistance of the side rail) divided by theinitial height of the absorber. A steel absorber operates by bundling.Once the folds of the absorber are in contact with one another, thecrushing force must increase so as to continue to deform the absorber.By contrast, for a composite absorber, the deformation is progressive:the material becomes delaminated as compression continues. A steelabsorber has a compaction ratio of around 75%, whereas an absorber madeof synthetic or composite material has a compaction ratio of 90%. Forexample, for a crushing travel of 100 mm, a steel absorber will be givena height of 135 mm and an absorber made of synthetic material will begiven a height of 110 mm, that is to say a gain of 25 mm, which is farfrom negligible in terms of motor car style. This allows the designergreater freedom when designing outer shapes f vehicles.

The beam according to the invention may furthermore have at least anyone of the following features:

the absorbers project from a rear face of the crossbar,

the absorbers extend opposite a rear face of the crossbar,

the absorbers are made of composite material,

the material of the absorbers comprises a plastic reinforced with glassfibers,

the crossbar has a profiled shape with a closed cross section,

the cross section has a rectangular or trapezoidal shape,

the cross section has an inner wall,

the absorbers are screwed to the crossbar,

the absorbers are integrally formed on the crossbar,

said material of the crossbar being an inner material, the crossbarcomprises an outer layer formed of the material of the absorbers,

the outer layer covers all of the inner material,

each absorber comprises a frustoconical body,

each absorber comprises two flat devises parallel to an axis of the bodyand contiguous to the body,

the devises project from the body along the axis of the body and are incontact with two faces of the crossbar, the body being in contact with athird face of the crossbar,

each absorber has a number of cells,

the cells form ducts which are parallel to one another,

the ducts extend perpendicular to a longitudinal direction of thecrossbar,

the ducts are vertical in the mounted position of the beam,

the cells are open at one end,

the cells have a profiled shape with a rectangular or trapezoidal crosssection,

the cells are arranged in rows and columns,

the absorbers project from and/or extend opposite two respective ends ofthe crossbar in a longitudinal direction of the crossbar,

the absorbers cover the two ends,

each absorber has an insert that penetrates into the crossbar, inparticular via an axial end of the crossbar, and

the material of the crossbar is a metal, for example steel or aluminum.

There is also provided according to the invention a bumper for avehicle, comprising a beam according to the invention. Preferably, thebumper will also comprise a skin and a compressible element locatedbetween the skin and the beam.

There is also provided according to the invention a vehicle chassiscomprising two side rails, one crossbar and two shock absorbers that areattached to the crossbar, fixed to the side rails and formed in amaterial that is different from the material of the crossbar, theabsorbers being made of synthetic material.

Finally, there is provided according to the invention a method ofproducing a bumper beam comprising one crossbar and two shock absorbersthat are formed in a material that is different from a material of thecrossbar, in which the absorbers are attached to two respective portionsof the crossbar, the absorbers being made of synthetic material.

The method may also have at least any one of the following features:

the beam is produced by extrusion,

the absorbers are integrally formed on the crossbar, and

the entire crossbar is covered with a material identical to that of theabsorbers.

Other features and advantages of the invention will become apparent fromthe following description of four embodiments given by way ofnon-limiting examples. In the appended drawings:

FIG. 1 is a perspective view of a first embodiment of the beam accordingto the invention, partially showing the side rails of the vehicle towhich it is attached;

FIG. 2 is a view in cross section of a bumper incorporating the beam ofFIG. 1;

FIG. 3 is a perspective view of one of the absorbers of the beam of FIG.1;

FIG. 4 is a view in section on IV-IV of the absorber of FIG. 3, with thescrew having been removed;

FIG. 5 is a view similar to FIG. 1, showing a second embodiment;

FIG. 6 is a perspective view of the crossbar of the beam of FIG. 5;

FIG. 7 is a perspective view from above of the left-hand end of the beamof FIG. 5;

FIGS. 8 and 9 are two views in cross section of the beam of FIG. 7, onVIII-VIII and IX-IX; and

FIGS. 10, 11 and 12 are, respectively, a perspective view from above, aperspective view from below and a side view of the absorber of FIG. 7.

FIGS. 1 to 4 show a first embodiment of the bumper according to theinvention. The bumper 2 comprises a beam 4 comprising one crossbar 6 andtwo shock absorbers 8 or “crash boxes”. The crossbar 6 is designed toextend horizontally and transversely to the direction of travel of thevehicle. The bumper may be a front bumper or a rear bumper. The crossbarhas an elongated overall shape that is slightly curved in the horizontalplane, the center of curvature being on the vehicle side.

The crossbar has a profiled shape. In cross section, the profile of thecrossbar is closed as shown in FIG. 2. The shape of this profile isusually rectangular or, as is the case here, trapezoidal. The crossbarcomprises a vertical rear wall 10 with a straight profile, an upper wall12 with an essentially horizontal straight profile, and a lower wall 14with an essentially horizontal straight profile parallel to the upperwall 12, these two walls being perpendicular to the rear wall 10. Thecrossbar has a front wall shaped in profile by two essentially straightsegments 16 a, 16 b that are inclined with respect to one another, thelower segment 16 a taking up most of the height and being inclineddownward whereas the upper segment 16 b is inclined upward and extendsover a smaller height. The front wall 16 extends from the upper wall 12to the lower wall 14. Moreover, the crossbar comprises a horizontalintermediate wall 18 that is essentially planar and extends atmid-height between the upper 12 and lower 14 walls from the rear wall 10to the front wall 16. It is possible for at least one of the horizontalwalls 12, 18 and 14 to have a slight waviness, which reduces itsresistance in the event of impact. In FIG. 2, the three walls have thiswaviness. The crossbar 6 is made of metal, preferably of aluminum orsteel.

With reference in particular to FIGS. 3 and 4, each absorber 8 comprisesa body 20 of frustoconical shape. The absorber comprises a plate 22 ofrectangular shape that is fixed at the end of the body 20 correspondingto the widest cone section. The plate 22 is perpendicular to the axis 36of the cone. The absorber 8 also comprises two devises 24 of essentiallytrapezoidal flat shape. Each clevis is fixed by one side 26 to the plate22. This side 26 has a cutout 28 in the shape of a parabola which givesthe clevis a fork-like overall shape. The two devises 24 extend parallelto one another and at a distance from one another on either side of thebody 20. Each fork 28 is fixed to the body 20. The plate 22 forms therear end of the absorber. Each clevis 24 has a front edge 30 that liesopposite the rear edge 26 and projects from the front end of the body 20in the direction of the axis 36. The plate 22 has orifices 32 havingaxes 34 parallel to the axis 36 of the cone.

The absorbers 8 are made, by molding, of synthetic material, preferablyof composite material. This will advantageously be a material comprisinga plastic reinforced with glass fibers, such as the material known asRTS (Reinforced Thermoplastic Sheet). Such a material, which is wellknown per se, is prepared from a stack comprising, alternately, layersof polypropylene and layers of glass fibers. This stack is heated andcompressed to form a contiguous plate. It is plates such as these whichare introduced into the mold for the purpose of producing each absorber8.

The bumper which has just been described is produced in the followingmanner. The absorbers 8 are produced as mentioned above. Furthermore,the crossbar 6 is produced by extruding metal through a suitably shapeddie. The profiled part thus obtained is sintered to give the crossbarits overall shape and the ends are finished.

The height of the crossbar from the upper face of the upper wall 12 tothe lower face of the lower wall 14 essentially corresponds to thedistance between the two front ends 30 of the devises 24. It istherefore possible to place each absorber 8 astride the crossbar 6. Inthis position shown in FIG. 1, the crossbar extends between the twodevises, the rear wall 10 of the crossbar being in contact with thefront end of the body 20. One or two orifices are provided on the frontend of each clevis and also at each relevant location on the crossbarfor the passage of a screw 40 which is designed to pass verticallythrough the entire height of the assembly by extending through the upperclevis 24, the upper wall 12, the intermediate wall 18, the lower wall14 and the lower clevis 24. In this way, each of the absorbers isrigidly fixed to the crossbar. The locations of the absorbers along thecrossbar 6 are close to the respective ends of the latter. Typically,each absorber 8 will be closer to the associated end than to the centerof the crossbar.

The absorbers 8 thus extend opposite the rear wall of the crossbar andproject from the latter in a direction perpendicular to the longitudinaldirection of the crossbar. The axes 36 of the absorbers are generallyparallel to one another.

Once the beam 4 has been thus formed with the crossbar 6 and theabsorbers 8, it is possible to mount said beam on the chassis of a motorvehicle. For this purpose, the plate 22 of each absorber is fixed to arespective one of the two side rails 42 of the vehicle which extendhorizontally from the front to the back in the direction of travel ofthe vehicle, parallel to one another and at a distance from one another.The absorbers are fixed to the ends of the side rails by means of screwswhich pass through the orifices 32.

The bumper also comprises a compressible element 44 which extends infront of the front wall 16 of the crossbar and in contact with thelatter. It also conventionally comprises a skin 46 that is made ofplastic or composite material and extends in front of the compressibleelement 44 so as to hide both this element and the beam and absorbersfrom view, as seen from outside the vehicle.

Another embodiment is shown in FIGS. 5 to 11. In said embodiment,elements that are similar to those of the first embodiment bearreference numbers increased by 100.

Here again, the bumper 102 comprises a beam 104 as well as acompressible element and a skin, the latter two being identical to thoseof the first embodiment and not having been shown. The beam 104comprises a crossbar 106 and two absorbers 108.

The crossbar 106 is of curved elongated shape and has a cross section ofclosed rectangular shape with no intermediate wall. Moreover, in thisembodiment, the front 116 and rear 110 walls extend upward and downwardbeyond the upper 112 and lower 114 walls, as shown in FIG. 6.

Instead of the body and the clevises, each absorber 8 has ribs 60 whichform a network of cells 62. In the present example, the cells 62 of eachabsorber are formed by ducts having their axes parallel to one anotherand perpendicular to the general direction of the crossbar. In thepresent case, the cells 62 are vertical when the bumper is in itsmounted position on the vehicle. Each absorber comprises in the presentcase three vertical flat ribs 60 a that extend essentially from thefront to the rear in the direction of travel of the vehicle and fourvertical flat ribs 60 b that extend in a direction essentially parallelto the crossbar so as to form a grid or a network with theaforementioned ribs 60 a. The ribs 60 b which are respectively foremostand rearmost connect between them the front and rear ends of the ribs 60a. The two other ribs 60 b constitute intermediate ribs. These ribs thusform, in plan view, a network of six cells 62 which form, as shown inFIG. 7, two columns of three cells and three rows of two cells, the rowsextending parallel to the crossbar. Each cell has, in plan view, anessentially rectangular or trapezoidal shape.

Each absorber is designed to be attached to the crossbar essentially atthe same location as the absorbers of the first embodiment. In thepresent case, the ends 64 of the crossbar 6 are perpendicular to thelongitudinal direction of the crossbar. The cells extend in the place ofthe cone and devises of the first embodiment. Each absorber alsocomprises a wall 66 that extends from the front rib 60 b along the rearwall 110 of the crossbar, in surface contact with the latter, and thenbends and extends toward the front so as to completely cover thecorresponding end 64 of the crossbar. Once it has reached the front wall116 of the crossbar, the wall 66 bends again so as to extend in thecontinuation of the crossbar in the longitudinal direction of thelatter. It then bends again so as to extend in a straight line obliquelyboth toward the rear and toward the absorber and reconnect with therearmost rib 60 b, the latter being extended in its plane beyond thecells.

Each absorber 108 comprises an intermediate wall 80 that is parallel tothe walls 112 and 114 of the crossbar and extends throughout theabsorber both in the cells 62 and opposite the associated end of thecrossbar.

Each absorber 108 furthermore comprises an insert 70 which is shown inparticular in FIGS. 10 to 12. This insert has a parallelepiped overallshape. It has a profile which allows it to penetrate into the end of thecrossbar 106 so as to form a male/female assembly with the latter. Theinsert 70 is fixed to the zone of the wall 66 that covers the end 64 ofthe crossbar. This insert has recesses 72 formed by ducts that areessentially parallel to the cells 62 and open at their two ends. It alsohas, at its center, a duct 74 for receiving a fixing screw, as will beseen below.

As in the previous embodiment, the crossbar 106 is made of metal whereasthe absorbers are made of composite material by molding. In order tomount the absorbers on the beam, the inserts 70 are introduced into therespective ends of the crossbar in accordance with a male/femaleassembly. A screw 76 is then introduced into orifices in the crossbarwhich have been made beforehand so as to extend in coincidence with theduct 74 of the insert, the screw passing through the upper wall 112 ofthe crossbar and then the duct 74 of the insert and finally the lowerwall 114 of the crossbar. This screw is immobilized in a suitable mannerby means of a nut.

The rear rib 60 b of each absorber performs a similar function to thatof the plates 22 of the previous embodiment. Thus, it is by means ofthis rib that each absorber 108 is fixed to the front end of the siderails 42 of the vehicle. It can therefore be seen, in this case too,that the absorbers are mounted on the crossbar by screwing and that theconnection to the structure of the vehicle is made by screwing theabsorbers to the side rails.

In a third embodiment of the invention, the absorbers 108 have a shapesimilar to that of the second embodiment but are integrally formed onthe ends of the crossbar 106. Consequently, a layer 80 of a materialidentical to the material of the absorbers covers the outside of theends of the crossbar 106. This layer has been shown in dashed line inFIG. 9. To produce the beam, the crossbar 106 is placed in the mold forproducing the absorbers and the latter are integrally formed on theends.

In a fourth embodiment of the invention, it may be provided that theentire crossbar 106 is covered with a layer of material 80 that isidentical to the material of the absorbers, as shown in FIG. 9.

In each of these embodiments, the closed shape of the cross section ofthe crossbar gives it sufficient rigidity to deform the test barrierduring the high speed impact compatibility test and to successfully passthis test. The absorbers provided with a body of frustoconical shapemake it possible to achieve a gain in terms of weight compared toabsorbers made of steel. Moreover, they have a compression ratio that isgreater than that of steel absorbers. These absorbers make it possibleto absorb the energy in a “reparability” impact.

In the second embodiment, the absorbers 108 also absorb the energyduring a reparability test and also protect the ends of the crossbar.Because they cover these ends and project from the latter in thedirection of the crossbar, they can deform in the event of a side impactand absorb the energy of the impact. The beam therefore responds betterin the event of a corner impact. Such a corner impact forms part of theparking impact specifications. In this embodiment, the weight gain iseven greater than in the first embodiment. Moreover, the crossbar mayhave a simpler shape than in the first embodiment for the purpose ofsimplifying extrusion thereof.

In the third embodiment, the absorbers may be integrally formed bycompression or injection molding on the ends of the crossbar. Thisembodiment has the advantage that it does not require parts assembly.

In the four embodiments, the crossbar may be made of aluminum, steel orof thermosetting or thermoplastic composite material. The absorbers mayalso be at least partly made of the material known as EMIR. In thismaterial, the glass fibers reinforcing the plastic are arranged in aglass fiber mat.

Of course, many modifications may be made to the invention withoutdeparting from the scope thereof. There may be provided a bumper beamfor a vehicle which comprises one crossbar and two shock absorbers thatare attached to respective portions of the crossbar, the crossbar havinga closed profile in cross section, independently of considerationsconcerning the materials of the crossbar and of the absorbers.

In the foregoing text, the screw fixings may be replaced by other fixingmethods.

1. A bumper (2) beam (4; 104) for a vehicle, comprising one crossbar (6;106) and two shock absorbers (8; 108) that are attached to tworespective portions of the crossbar and are formed in a material that isdifferent from a material of the crossbar, characterized in that theabsorbers are made of synthetic material.
 2. The beam as claimed inclaim 1, characterized in that the absorbers (8; 108) project from arear face (10; 110) of the crossbar (6; 106).
 3. The beam as claimed ineither of claims 1 and 2, characterized in that the absorbers (8; 108)extend opposite a rear face (10; 110) of the crossbar.
 4. The beam asclaimed in any of claims 1 to 3, characterized in that the absorbers (8;108) are made of composite material.
 5. The beam as claimed in any ofclaims 1 to 4, characterized in that the material of the absorberscomprises a plastic reinforced with glass fibers.
 6. The beam as claimedin any of claims 1 to 5, characterized in that the crossbar (6; 106) hasa profiled shape with a closed cross section.
 7. The beam as claimed inclaim 6, characterized in that the cross section has a rectangular ortrapezoidal shape.
 8. The beam as claimed in any of claims 1 to 7,characterized in that it has an inner wall (18).
 9. The beam as claimedin any of claims 1 to 8, characterized in that the absorbers (8; 108)are screwed to the crossbar (6; 106).
 10. The beam as claimed in any ofclaims 1 to 9, characterized in that the absorbers (108) are integrallyformed on the crossbar (106).
 11. The beam as claimed in any of claims 1to 10, characterized in that, said material of the crossbar (106) beingan inner material, the crossbar comprises an outer layer (80) formed ofthe material of the absorbers (108).
 12. The beam as claimed in claim11, characterized in that the outer layer (80) covers all of the innermaterial.
 13. The beam as claimed in any of claims 1 to 12,characterized in that each absorber (8) comprises a frustoconical body(20).
 14. The beam as claimed in claim 13, characterized in that eachabsorber (8) comprises two flat devises (24) parallel to an axis (36) ofthe body and contiguous to the body.
 15. The beam as claimed in claim14, characterized in that the Devises (24) project from the body alongthe axis (36) of the body and are in contact with two faces (12, 14) ofthe crossbar (6), the body being in contact with a third face (10) ofthe crossbar.
 16. The beam as claimed in any of claims 1 to 15,characterized in that each absorber (108) has a number of cells (62).17. The beam as claimed in claim 16, characterized in that the cells(62) form ducts which are parallel to one another.
 18. The beam asclaimed in claim 17, characterized in that the ducts extendperpendicular to a longitudinal direction of the crossbar.
 19. The beamas claimed in claim 17 or 18, characterized in that the ducts arevertical in the mounted position of the beam.
 20. The beam as claimed inany of claims 16 to 19, characterized in that the cells (62) are open atone end.
 21. The beam as claimed in any of claims 16 to 20,characterized in that the calls (62) have a profiled shape with arectangular or trapezoidal cross section.
 22. The beam as claimed in anyof claims 16 to 21, characterized in that the cells (62) are arranged inrows and columns.
 23. The beam as claimed in any of claims 1 to 22,characterized in that the absorbers (108) project from two respectiveends (64) of the crossbar (106) in a longitudinal direction of thecrossbar.
 24. The beam as claimed in any of claims 1 to 23,characterized in that the absorbers (108) extend opposite two respectiveends (64) of the crossbar (106) in a longitudinal direction of thecrossbar.
 25. The beam as claimed in claim 23 or claim 24, characterizedin that the absorbers (108) cover the two ends.
 26. The beam as claimedin any of claims 1 to 25, characterized in that each absorber (108) hasan insert (70) that penetrates into the crossbar (106), in particularvia an axial end of the crossbar.
 27. The beam as claimed in any ofclaims 1 to 26, characterized in that the material of the crossbar (6;106) is a metal, for example steel or aluminum.
 28. A bumper (2) for avehicle, characterized in that it comprises a beam as claimed in any ofclaims 1 to
 27. 29. The bumper as claimed in claim 28, characterized inthat it also comprises a skin (46).
 30. The bumper as claimed in claim29, characterized in that it also comprises a compressible element (44)located between the skin (46) and the beam (6).
 31. A vehicle chassiscomprising two side rails (42), one crossbar (6; 106) and two shockabsorbers (8; 108) that are attached to the crossbar, fixed to the siderails and formed in a material that is different from a material of thecrossbar, characterized in that the absorbers are made of syntheticmaterial.
 32. A method of producing a bumper beam (4; 104) comprisingone crossbar (6; 106) and two shock absorbers (8; 108) that are formedin a material that is different from a material of the crossbar, inwhich the absorbers are attached to two respective portions of thecrossbar, characterized in that the absorbers are made of syntheticmaterial.
 33. The method as claimed in claim 32, characterized in thatthe beam (4; 104) is produced by extrusion.
 34. The method as claimed ineither of claims 32 and 33, characterized in that the absorbers (108)are integrally formed on the crossbar (106).
 35. The method as claimedin any of claims 32 to 34, characterized in that the entire crossbar(106) is covered with a material identical to that of the absorbers(108).